This invention concerns a method and a circuit arrangement for monitoring the amplitude of sine-shaped signals, taken from a scan of an object which is to be measured or controlled. The signals are obtained both from static and from dynamic operation.
Signals of this type are used in counting and control circuits. It is therefore necessary that the amplitude of these signals be monitored within a level range, so that satisfactory functioning of such circuits is assured.
For example, an apparatus for contamination indication in a length measuring apparatus is known, where a special circuit monitors the amplitude of photo-receptor signals. Before the magnitude of the signal of the received signals drops due to contamination of the scale far enough that erroneous counting is possible, there is an optical indication, which shows that the rectified signal, obtained from scanning the scale and compared with a reference potential demonstrating the desired signal level, has dropped below it.
It is the disadvantage of this solution that signals (with f&gt;0) are obtained only in dynamic operation. In static operation (stopped position), there is an erroneous indication.